Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This applica-tion is a divisional of App1ica-tion
Serial No. 395,233, filed January 29, 1982.
The present inverltion relates generally to
a method and apparatus for flotation separation of the
components of a slurry and more particularly pertains
to an improved method and apparatus for beneiciating
coal by flotation separation of a froth utilizing a
spray nozzle such that ground coal particles may be
separated from impurities associated therewith such
as ash and sulfur.
Coal is an extremely valuable natural resource
in the United States,as well as the remainder of the
world,because of its relative abundance. It has been
estimated that the United States alone has more energy
available in the form of coal than in the co~bined natural
resources of petroleum, natural gas, oil shale, and tar
sands. Recent energy shortages, together with the avail-
ability of abundant coal reserves and the continuing
uncertainties regarding the availability of crude oil,
have made it i~perative that methods for converting coal
into a more useful energy source be developed.
Known prior art processes for froth flotation
separation of a slurry of particulate matter are based
on constructions wherein air is introduced into the
liquid slurry of the particulate matter as, e.g. through
a porous cell bottom or a hollow impeller shaft, thereby
producing a surface froth. These prior art methods are
relatively inefficient approaches especially hhen large
concentrations of particulate matter are being processed.
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1 Generally, these techniques are inefficient in providing
sufficient contact area between the particulate rnatter
and frothing air. As a result large amounts of energy
can be expended in frothing. In addition, froth flotation
techniques which permit bubbles to rise in the slurry can
tend to trap an~ carry impurities, such as ash in the
froth slurry, and aceordingly the resultant beneficiated
partieulate produet ean have more impurities therein than
neeessary.
Methods have been suggested and are being explored
in the benefieiation of coal, i.e., the cleaning of eoal of
impurities sueh as ash and sulfur, either prior to burning
the coal or after its combustion. In one recently developed
teehnique for benefieiation, termed hereinehemieal surfaee
treating, raw eoal is pulverized to a fine mesh size and
is then ehemically treated. Aecording to this technique
the treated coal is then separated from ash and sulfur,
and a beneficiated or cleaned coal produet is reeovered
therefrom.
In further detail, in the heretofore mentioned
ehemiealsurEaee treating proeess coal is first cleaned of
roek and the like, and is then pulverized to a fine size
of about 48 to 300 mesh. The extended surfaees of the
ground eoal partieles are then rendered hydrophobie and
oleophilie by a polymerization reaetion. The sulfur and
mineral ash impurities present in the eoal remain hydro-
philie and are separated from the treated eoal produet
in a water washing step. This step utilizes oil and
water separation teehni~ues, and the eoaliparticleci made
3 hydrophobie~ can float in recovery on a water phase whieh
eontains hydrophilie impurities.
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1 In accordance wi-th the teachings herein, the
present invention provides an improved method and appara-
tus for froth flotation separation of the components of
a slurry having particulate matter therein which is to be
separated. In this arrangement, at least one primary
spray nozzle is positioned above a flota~ion tank h~ving
a liquia bath therein, and sprays an input slurry con-
taining particulate matter through an aeration zone into
the surface of the liquid. The spraying operation creates
a froth on the surface of the liquid in which a quantity
of the particulate matter is floating, such that the
~roth containing the particulate matter can be removed
from the water surface as a separated product. Other
components of the slurry and a minor quantity of particu~
later matter sink in the liquid bath.
Thus, in one embodiment of the present invention,
a collector trough is positioned in the tank below the
primary spray nozzle~s) for collecting the sinking
materials. The collected materials are then recycled to
at least one recycle spray nozzle positioned above the
tank which resprays them through an aeration zone into
the liquid surface. Therefore,in this embodiment, the
present invention operates in an efficient manner by
providing a recycling operation wherein particles which
do not float after being sprayed through a primary spray
nozzle are recycled to a further spray nozzle to provlde
a second opportunity for recovery. In a further embodi-
ment,the recycle spray nozzle(s) is positioned in proximity
to the primary spray nozzle(s), and a vertical baffle
3 plate is positioned in the tank between the primary and
recycle nozzles to provide separation for materials sink-
in~ from the sprays of the respective nozzles.
n acco:rdance with further details of -the
present invention, the spray nozzle(s) utilized herein
is preferably a hollow jet cone nozzle defining an approxi-
mately 30 spray pattern. Further, the slurry is preferably
supplied to the nozzle in a pressure range of from 5 to
40 psi,and more prefereably in the range of from 15 to
20 psi. Also, the present invention has particular
utility to a coal beneficiation operation for froth
flotation separation of a slurry of coal particles and
associated impurities.
The present invention operates in a manner which
is more efficient than prior art arrangements because of
the unique manner of froth generation in which the slurry
is sprayed through an aeration zone. Moreover, further
uni~ue efficiency is provided by more effective cleaning
of particulate matter such as coal and higher product
recoveries by providing that those particles which do
not initially float are resprayed into the water surface
to promote and provide a high probability of secondary
recovery of the product from waste materials.
In accordance with further details of ano-ther
embodiment of the present invention, a skimmer arrange-
ment having a plurality of spaced skimmer plates depend-
ing from a conveyor is arranged along the top of the tank
to skim the resultant froth therefrom. An upwardly
inclined surface extends from the water surface in the
tank to a collection tank arranged at one side of the
flotation tank, and Lhe skimmer plates skim the froth
from the water surface up the inclined surface and into
the collection tank. Moreover, in one embodiment the
primary and recycle spray nozzles are inclined from
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1 the verticle in t~e direction in which the skimmer arrange-
ment operates to direct the flow of froth in that direction
along the water surface. Settling impurities are removed
from ,he flotation tank by a circulating arrangement opera-
ting near the bottom of the collection tank which xemovesboth water and settling impuritiesr
While the froth flotation system of the present
invention is described in detail herein in the context of
a coal beneficiating operation, it is apparent that the
teachings herein have direct applicability to other appli-
cations of froth flotation separation technology. For
instance, the froth flotation separation techni~ues dis~
closed herein can be utilized in conjunction with particu-
late matter such as carbonaceous particles, noncarbonaceous
particles, or mixture of both, mine tailings, oil shale,
residuals, waste particulates, mineral dressings, graphite,
mineral ores, fines, etc.
The foregoing advantages of the present
invention for an arrangement for froth flotation
separation may be more readily understood by one skilled
in the art with reference being had to the following
detailed description of several preferred embodiments
thereof, taken in conjunction with the accompanying draw-
ings wherein like elements are designated by identical
reference numerals throughout the several drawings, and
in which:
Figure 1 is an elevational view of a schematic
exemplary embodiment of a flotation arrangement constructed
pursuant to the teachings of the present invention;
Figure 2 illustrates an elevational view of another
flotation tank utilizing the invention herein;
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1 ~igure 3 is a partially sectional elevational
view of one type of spray no~zle which can be utilized in
the embodiments of Figures 1, 2 and 4; and
Figure ~ illustrates an elevational view of a
more detailed embodiment of a flotati~n tan]c constructed
pursuant to the teachings herein.
The apparatus and method of -the present inven-
tion is adapted to the separation of a wide variety of
solid-fluid streams by the creation of a solids contain-
ing froth phase, and is suitable for the separation of
many types of particulate matter. U.~. Patent No. 4,30~,573
may be referred to for further details on the chemical
processes which are particularly useful in conjunction
with the subject invention.
The present invention is described herein with
reference to a coal beneficiating operation as disclosed, for
example, in detail in the aforementioned U.~. patent. Thus,
referring to the drawings herein in greater detail, Fig. 1
illustrates a first embodiment 10 of the ~resent invention
having a flotati~n tank 12 filled with water to level 14.
In operation,a slurry of finely ground coal particles,
associated impurities, and if desired additional additives,
such as monomeric chemical initiators, chemical catalysts
and fluid hydrocarbons is sprayed through at least one
primary spray nozzle 16 positioned at a spaced apart dis-
tance above the water level in tank 12. In alternative
embodiments, two or more nozzles can be usecl to spray
slurry and/or any other desired ingredients into the tank.
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1 I~he strearn of treated coal i5 pumped under pres-
sure through a manifold to the sprav no7zle 16 wherein the
resultant shearing forces spray the coal flocculent slurry
as fine droplets such that they are forcefully jetting into
the mass of a continuous water bath in tank 12 to form a
froth 17. High shearing forces are created in nozzle 16,
and the dispersed particles forcefully enter the surface
of the water and break up the coal-oil-water -flocs thereby
water-wetting and releasing ash from the interstices between
the coal flocs and breaking up the coal flocs so that
exposed ash surfaces introduced into the water are separated
from the floating coal particles and sink into the water
bath. The surfaces of the finely divided coal particles
now contain air sorbed in the atomized particles, much
of which is entrapped by sprayiIIg the slurry through an
aeration zone 19 such that air i5 sorbed in the sprayed
slurry. The combined effects on the treated coal cause
the flocculated coal to decrease in apparent density and
to float as a froth 17 on the surface of the water ba-th.
The hydrophilic ash remains in the bulk water phase, and
tends to settle downwardly in tank 12 under the influence
o~ gravity. Tank 12 in Figs. 1, 2 and 4 may be a conven-
tional froth flotation tank commercially available from
KOM-LINE-Sanderson Engineering Co., Peapack, N.Y. modified
as set forth below. The flotation tank can also include
somewhat standard equipment which is not illustrated in
the drawings such as a liquid level sensor and control
system and a temperature sensing and control system.
The present invention operates on a froth
generation princiPle in which the slurry is sprayed through
an aeration zone such that substantial quantities of air
a esorbed by the sprayed fine droplets of the slurry.
Accordingly,air is introduced into the slurrv in a unique
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1 manner to generate the resultant froth. The advantages
of this manner of froth generation make the teachings
herein particularly applicable to froth flotation separa-
tion of slurries which have a substantial proportion
of particulate matter therein.
The coal particles in the floating froth 17
created by nozzle 16 -can be removed from the water sur-
face by,e.g., a s}ci~ming arrangement 28 in which an endless
conveyor belt 30 carries a plurality o spaced skimmer
plates 32 depending therefrom. The skimmer plates are
pivotally attached to the conveyor belt to pivot in two
directions relative to the belt, and the bottom run of
the belt is positioned above and parallel to the water
surface in the .ank. The plates 32 skim the resultant
froth on the water surface in afirst direction 34 toward
a surface 36, preferably upwardly inclined, extending
from the water surface to a collection tank 38 arranged
at one side of the flotation tank, such that the skimmer
plates 32 skim the froth from the water surface up the
surface 36 and into the collection tank 38.
In the arrangement of the disclosed embodiment,
the waste disposal at the hottom of the tank operates in
a direction 40 flowing from an influent s-tream ~2 to the
effluent stream 26, while the skimmer arrangement at the
top of the tank operates in direction 34, counter to that
ofthe waste disposal arrangement. Although the illustrated
embodiment shows a counterflow arrangement, alternative
embodiments are contemplated within the scope of the Pre-
sent invention having, e.g., cross and concurrent flows
therein.
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1 Figure 3 is a partially sectional view of one
type of commercially available spray nozzle 64 which may
be used in conjunction with the systems shown in ~igures
1, 2 and 4. A recessed threaded couplin~ 66 is provided
to attach the nozzle to a primary or recycle manifold
supplying the nozzle with slurry under pressure. The
slurry encounters a frustoconical venturi section 68
which accelerates the flo~ veloci~y thereoL according to
the well known venturi effect. The slurry then flows
through the nozzle aperture having a nominal diameter 70,
which in combination with a diverging section 72 defines
a hollow cone spray pattern 74 having an encompassing spray
angle 76. In one preferred embodiment of the present
invention, angle 76 is approximately thirty deqrees,
although other angles which provide the herein contem-
plated results are included within the scope of this
invention.
Spray nozzle 64 ~ay be a hollow jet nozzle as
is commercially available from Sprayin~ Systems Co.,
Wheator., Illinois. Of course, it is contemplated herein
that other types of nozzles, which function to provide
the desired resl~lts as hereinbefore described, may also
be used. The nozzles are preferably constructed o~
stainless steel, ceramic or other suitable hard metal
to avoid erosion by the various particles in the .slurry
being pumped therethrough. The nozzles are preferably
supplied with slurry in the supply manifolds at a p.res-
sure in the range of 5 to 40 psi, and more preferably
in a pressure range of 15 to 20 PSi.
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l Each nozzle 16 may be -tilted at an angle ~ with
respect to a vertical, ~i.e., the position o-f the nozzle
relative to the liquid surface level), as shown in Figure 4
such that it functions to direct the flow of froth in a
direction towaxds the skimmer arrangement 28. However, the
angle of incidence ~ ~oes not appear to be critical, and
the vertical positioning shown in Figure l may be preferred
to create a condition most conducive to ayitation and froth
generation at the water surface. It appears to be signif-
icant that the agitation created by the nozzle sprays definea zone of turbulence extending a limited distance beneath
the water surface level. Too much turbulence may actually
reduce the amount of frothing produced at the water sur-
face. Among other means, the depth of the turbulence
zone may be adjusted by varying the supply pressure of
the slurry in the supply manifolds and also the distance
of the nozzles above the water surface. In one operative
embodiment, a zone of turbulence extending two to four
inches beneath the water surface producesvery good aaita-
tion and froth generation, although the distance is depen-
dent on many variables such as the tank size, the medium
in the tank, etc. and accordingly may vary considerably in
other embodiments.
In one operation utiliæina the present invention
as shown in Fig. 2, a recycling technique is employed to
further improve the efficency relative to prior art arrange-
ments. In the recycling technique, coal particleswhich
do no float after being spraved through a spray nozzle 16,
designated a primary spray nozzle in context with this
3 embodiment, are recycled to a further recycle spray nozzle l~
to provide the coal particles a second opportunity for
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1 recovery. In this arrangement a collector trough 20,
preferably in the form of an open hemispherical pipe,
is positioned in t~nk 12 beneath the primary spray noz-
zle(s) 1~ for collecting the sinking materials. A pump
22 is coupled to trough 20 and functions to draw settling
materials into the trough from which it is pumped under
pressuré to the recycle spray nozzle(s). At least one
recycle spray nozzle 18, which may be the same type of
nozzle as primary spray nozzle 16, is provided above the
tan]c for respraying into the surface of the water bath
the materials collected by the trough such tha-t coal
particles collected therein are recycled and a portion
of the recycled coal ~loats as a froth on the water
surface an additional time and is recovered. The recycled
spray nozzle(s) 1~ is positioned in proximity to the pri-
mary spray nozzle(s) 16, and a vertical baffle plate 2~
is positioned in the tank 12 between primary and recycle
nozzles to provide separation for materials sinking from
the sprays of the respective nozzles. In alternative
embodiments,~urther stages of recycling may be provided
by adding additional troughs and recycle noæ~les in the
tank.
This arrangement results in an efficient opera-
tion, providing more effective cleaning of the coal and
higher product recoveries by providing that coal particles
which do not initially float have a high probability of
being resprayed onto the water surface to promote secondary
recovery of the product from waste materials.
After the recycling operation, the materials
3 which sink from the recycle spray tend to settle do~n-
wardly in tank 12 under the influence of gravity, and
are withdrawn in an ash-water stream 26 from the base of
the vessel.
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1 Figure 4 illustrates an eleva-tional view of a
more detailed illustration of another emhodiment oE a
flotation arrangement 46 pursuant to the teachings herein.
Tank 12 may be a conventional froth flotation tank com-
mercially available from KO~-LINE-Sanderson Engineering
Col, Peapack, N.J. modified as set forth below. The base
of the tank can oe supported in a conventional manner by
channel and flanged structural members, as illustrated.
The flotation tank can also include somewhat standard
equipment which is not illustrated in the drawings such
as a liquid level sensor and control system and a tempera-
ture sensiny and control system.
The conveyor system in this embodiment includes
a drive roller 48 at one end, driven by a chain or equiva-
lent linkage ~rom a skimmer drive 50 mounted on the tank.The other end of the conveyor is defined by an idler
roller 52 which in combination with a second idler roller
54 defines a horizontal run for the conveyor along the top
of the flotation tan~. The conveyor belt in this design
is defined by two strands of two inch, double pitch chain
with each strand having ninety-six pitches. Twelve
skimmex plates are ~arried by the two chains, with each
plate being eight pitches apart on the two conveyor chains.
The bottom run of the conveyor arrangement is positioned
approximately ten inches above the water surface, and
each plate depends downwardly from the conveyor chains
appxoximately ten inches to the water surface. The
skimmer plates carry the coal bearing froth up an
inclined surface 36 to a chute 37 through which the froth
is directed to a collection tank.
Trough 20 is in the form of an open hemispherical
pipe positioned below the area at which the spray from the
primary spray nozzle 16 impinges on the water, and is coupled
by lengths of vertical and horizontal conduits 60 and 62 to
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1 pump 22, not shown in Figure 2, which in ~urn suppli.es
recycle manifold 58 with a slurry at a preferred feed
pressure.
While several embodiments and variations of
a method and apparatus for froth flotation separation of
the components of a slurry have been described in detai.l
herein, it should be apparent that the teachings and
disclosure of the present patent will suggest many other
embodiments and variations to those skilled in this art.
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